Thermoelectric device with a plurality of modules individually controlled

ABSTRACT

A heating and cooling apparatus having a first gas conduit, a second gas conduit and at least one thermoelectric module. In a first embodiment, structure is provided to introduce moisture into the second gas conduit, upstream of that conduit&#39;s association with the thermoelectric module. The introduction of the moisture into the gas within the second gas conduit functions to decrease the temperature between the temperature of the gas in the first conduit and the temperature of the gas in the second conduit, thereby optimizing the operation of the thermoelectric module. In a second embodiment a plurality of thermoelectric modules are arranged in an array and positioned between the gas conduits and associated therewith. The power supplied to each of the thermoelectric modules is adjusted to correspond to an optimum power input calculated for each thermoelectric module respectively. This calculation utilizes a temperature differential between the temperature of the thermoelectric material at the junction of the thermoelectric module with the first gas conduit and the temperature of the thermoelectric material at the junction of the thermoelectric module with the second gas conduit.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.07/982,351 filed Nov. 27, 1992 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is in the field of thermoelectric devices. The inventionhas special application to thermoelectric devices for heating andcooling air for human use which utilize thermoelectric modulesassociated with a heat exchanger.

2. State of the Art

Thermoelectric devices for heating and cooling based upon the peltiereffect are well known in the prior art. Typically, a thermoelectricmodule is constructed of N-type and P-type semiconductor material, suchas bismuth telluride. The N-type and P-type semiconductor material areelectrically connected in series. When an electric current is passedthrough the circuit, heat is absorbed at the cold junction of thecircuit and is transferred to the hot junction of the circuit. Byassociating the hot and cold junctions with a heat exchanger, heat canbe transferred from one flow stream to another. Typically, the heatexchanger is filled with either gas or liquid media, thereby resultingin the heating of one media and the cooling of the other media.

Historically, practical applications of thermoelectric cooling andheating using thermoelectric modules have been primarily limited tosmall scale specialized uses because of high cost and energyinefficiencies. In the last 15 to 20 years, applications ofthermoelectric modules have been developed to utilize them in largescale cooling of submarines and passenger trains. Utilization ofthermoelectric modules in large scale applications has requireddevelopment of various types of thermoelectric devices, which utilizethermoelectric modules associated with heat exchangers, which aredesigned for assembly with each other to provide the cooling and heatingcapacity required for large scale applications. One such prior artdesign for a thermoelectric device includes a parallel flow heatexchanger in association with thermoelectric modules. Another prior artdesign for a thermoelectric device is the "air to air cross-flow" designin which the conduits of the exchanger, which sandwich thermoelectricmodules, are positioned relative to each other to allow forperpendicular flow of hot and cold air through the thermoelectricdevice. Typical of these thermoelectric devices are U.S. Pat. No.3,626,704 issued to Coe on 9 Jan. 1970 and U.S. Pat. No. DE 1,801,768issued to Newton in 1967.

The primary disadvantages of these prior art devices are lack ofreliability and difficulty of service. In some prior art devices theelectric current to the thermoelectric modules flows through the heatexchanger itself. To establish the electric circuit, the thermoelectricmodules are electrically connected in series through the heat exchanger.In some prior art configurations, the electric connection is establishedby attaching a heat exchanger to the hot and cold junctions of thethermoelectric modules by soldering, thereby creating rigid physicalconnections between adjacent thermoelectric modules and between the heatexchanger. Since the heat exchanger conduit attached to the hot side ofthe thermoelectric modules and the heat exchanger conduit attached tothe cold side of the thermoelectric modules are subject to differenttemperatures, they are expanding and contracting at different rates.This expansion and contraction differential creates a shear force acrossthe thermoelectric modules, which may result in their breakage.

In an attempt to overcome these problems, a design, such as thattypified by U.S. Pat. No. 3,726,100 issued to Widakowich on 10 Apr. 1973was developed. In this design, the heat exchanger conduits are notsoldered to the thermoelectric module, but the thermoelectric modulesare sandwiched between the hot and cold heat exchanger conduits, withthe hot and cold heat exchanger conduits compressed against adjacentthermoelectric modules by bolts such that the heat exchanger conduitsare in electric and thermal contact with the thermoelectric modules tocreate an electric circuit through the heat exchanger conduits andsemiconductor material such that they are connected in series. Sinceadjacent thermoelectric modules are still rigidly connected to eachother, the shearing forces still exist to some extent.

BRIEF SUMMARY OF THE INVENTION

A heating and cooling apparatus adapted for treating a fluid, such as agas is disclosed. The apparatus is specifically adapted for use inheating or cooling air for human use, e.g. for breathing. The apparatusincludes a first fluid conduit configured to direct the flow of a firstfluid. In a preferred embodiment of the invention this first fluid isair, although the first fluid could also be another gas or a liquid.

A second fluid conduit, configured to direct the flow of a second fluid,is positioned spacedly from the first fluid conduit. In preferredconstructions this second fluid is also air, although the second fluidmay also be another gas or a liquid. A thermoelectric means ispositioned between the first and second fluid conduits to be operablyassociated with each of the two conduits. The thermoelectric means isadapted to transfer heat from the first fluid in the first fluid conduitto the second fluid in the second fluid conduit, thereby cooling thefirst fluid and rejecting heat into the second fluid at a highertemperature.

In those embodiments of the invention wherein the fluid within thesecond conduit is a gas, hereinafter referred to as the "second gas,"the second fluid conduit is fitted with a moisture introduction meansadapted for introducing a liquid, such as water, into the second gas.The moisture means may be adapted to introduce this liquid into thesecond fluid conduit at a location in that conduit which is upstream ofthe conduit's association with the thermoelectric means.

The moisture, i.e. the liquid, in the second gas flow absorbs heat fromthe second gas, thereby lowering the temperature of the second gas priorto the second gas coming into contact with that region of the secondfluid conduit which contacts the thermoelectric means. When the quantityof heat corresponding to the latent heat of vaporization of the liquidhas been absorbed by the liquid, the liquid undergoes a phase changefrom liquid to gas, i.e. to vapor. As the moisture changes from a liquidto a gas, the liquid absorbs energy while decreasing the dry-bulb airtemperature of the second gas flow. This phenomena, in turn, tends tominimize the temperature differential between the temperature of thefluid in the first fluid conduit and the temperature of the second gasin the second fluid conduit.

In one embodiment of the invention specifically adapted for heating orcooling air for human use, the first fluid and the second fluid are bothgases. Preferably, both gases are ambient air. These gases shallhereinafter be referred to as the first gas and the second gas. It hasbeen found that the use of a moisture introduction-means in the secondconduit is very beneficial in this particular embodiment in minimizingthe aforedescribed temperature differential.

The correlation of the thermoelectric material temperature with theconduit fluid temperature can be related to a thermal resistance whichis a function of base material conduction, airflow rate and convectioncoefficient. Generally speaking, the two temperatures would be within 15degrees Celsius of each other. Accordingly, it should be understood thatthe temperature of the first gas flow corresponds generally within 15degrees Celsius to the actual temperature of the thermoelectric materialat the junction of the thermoelectric module and the first conduit. Thetemperature of the second gas flow also corresponds, within generallywithin 15 degrees Celsius to the actual temperature of thethermoelectric material at the junction of the thermoelectric module andthe second conduit.

It follows that lowering the dry bulb temperature of the second gas flowby use of the moisture introduction means previously described willcontribute to a lower temperature of the thermoelectric material at thejunction of the thermoelectric module with the second conduit. The lowerthermoelectric material temperature will in turn tend to minimize thetemperature differential between the two junctions previously described.

It has been found that thermoelectric means of the type utilized in thisinvention achieve optimal operation when the temperature differentialbetween the two junctions is minimized. The minimization of thetemperature differential, by means of the introduction of liquid intothe second gas flow, upstream of that gas flow's contact with thethermoelectric means therefore increases the efficiency of thethermoelectric means and therefore the efficiency of the heating andcooling system in general.

In another embodiment of the invention, provisions are made forcontrolling the operation of individual thermoelectric means or discretegroups of such thermoelectric means. In one construction thethermoelectric means includes a plurality of thermoelectric moduleswhich are spacedly positioned from each other and preferably arranged inan array. Each of the thermoelectric modules, or in some instances eachgroup of thermoelectric modules, is connected to a power supply means sothat the quantity of power supplied respectively to each module, orgroup of modules, may be individually controlled. The quantity of powerto be supplied to each module is determined by calculating or estimatingthe temperature differential between the temperature of thethermoelectric material at the junction of the thermoelectric modulewith the first fluid conduit and the temperature of the thermoelectricmaterial at the junction of the thermoelectric module with the secondfluid conduit. The temperature differential so calculated or estimatedis then utilized to calculate the input current which would produce theoptimal performance of the thermoelectric module, or group of modules,for the given conditions and cooling power requirements.

A power regulation means is utilized to control the respective quantityof current supplied to each thermoelectric module. In preferredconstructions the power regulation means provides a quantity ofelectrical current to each module or group of modules corresponding tothe respective optimal quantity of current calculated for each module,or group of modules.

In some embodiments, the invention may include a sensing means foractually sensing the temperature of the thermoelectric material at eachof the two junctions previously described. Alternatively, the inventionmay include a sensing means adapted for sensing temperatures of otherelements of the apparatus or the fluids treated thereby to provide datafrom which the temperatures of the thermoelectric material may beestimated. For example, the temperature of the fluid flows, either atlocations within the conduits or at the inlets and outlets of thoseconduits may be sensed. Alternatively, the temperature of the conduitsidewalls may be sensed.

The invention may also include the use of an automated control systemwhereby the temperature readings sensed by the sensing means may beperiodically or continuously monitored during the operation of theapparatus. The automated control system may include computation meansadapted to receive the temperature readings from the sensing means andthereafter calculate a temperature differential across one or more ofthe thermoelectric modules. In a preferred construction, the computationmeans and the sensing means are adapted to sense temperatures of all thethermoelectric modules and thereafter calculate a temperaturedifferential for each thermoelectric module. This calculation may beperformed either periodically or continuously during the operation ofthe apparatus. The computation means may further be adapted, e.g.programmed, for determining the optimal power input for each respectivethermoelectric module, or group of modules, based on the respectivetemperature differential determined for that thermoelectric module, orgroup of modules.

The power regulation means may be operatively associated with thecomputation means. The power regulation means is adapted to regulate oradjust the power being supplied to each of the respective thermoelectricmodules, or group of modules, to accord with the optimal power inputdetermined by the computation means for each specific module. The powerregulation means may be adapted for adjusting the power input to therespective thermoelectric modules, or groups of modules, either on acontinuous or semi-continuous basis.

In order to further enhance the operation of the apparatus, the fluidflow rate through either the first or second conduits or both conduitsmay be varied responsive to thermal loads and ambient conditions. Thefluid flow rate may be controlled by adjusting the size of the fans,pumps or other fluid conveyance means or alternatively, adjusting thequantity of power supplied to such conveyance means.

The embodiment of the invention which utilizes means of regulating thepower supplied to the various thermoelectric modules may also be fittedwith the moisture introduction means previously described as part of thepreviously described embodiment.

In the embodiments previously described the thermoelectric means mayinclude at least two thermoelectric modules, each module having a firstside and a second side wherein the first sides of the thermoelectricmodules are in parallel thermal contact with the first fluid conduit,and the second fluid conduit which is divided into sections wherein eachsection of the second conduit is in thermal contact with the second sideof only one thermoelectric module. This configuration provides forindependent "flotation" of the sections of the second conduit on thefirst conduit so that each of the sections of the second conduit expandand contract independent of each other, thereby minimizing the shearforce exerted on the thermoelectric module which is between each sectionof the second conduit and the first conduit. Preferably there is a meansfor compressing the section of the second conduit, the thermoelectricmodule that is in thermal contact with the section of the second conduitand the first conduit to achieve optimum thermal transfer between thesection of the second conduit and the first conduit.

A plurality of thermoelectric devices may be associated with one anotherto assemble a thermoelectric subunit. A plurality of thermoelectricsubunits may then be removably associated with each other to assemble athermoelectric apparatus having the required heating or coolingcapacity. Preferably the orientation of the flow channels of the firstconduit to the flow channels of the sections of the second conduit areperpendicular to each other to provide for the flow of the media beingheated or cooled in a cross-flow design.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially exploded view of a thermoelectric subunitassembled from a plurality of thermoelectric modules;

FIG. 2 is a partially exploded view of a layer of two thermoelectricsubunits assembled from a plurality of thermoelectric modules;

FIG. 3 is a perspective view of a thermoelectric apparatus assembledfrom two layers of thermoelectric subunits as illustrated in FIG. 2;

FIG. 4 is a cross-section of one thermoelectric subunit along sectionalline 4--4 of FIG. 3;

FIG. 5 is a schematic showing an application of the invention for largescale cooling and heating of an aircraft, including the passengerboarding bridge associated therewith;

FIGS. 6 and 6a are side views of a first fluid conduit, one or morethermoelectric modules and a second fluid conduit;

FIG. 7 is a graph depicting the temperature of the gas in the firstconduit and the temperature of the gas in the second conduit at variouslocations along the respective lengths of the aforesaid conduits;

FIG. 8 is a graph depicting the heat pumping capacity of an individualthermoelectric module as a function of the current passing through thethermoelectric module for various temperature differentials;

FIG. 9 is a graph which illustrates the coefficient of performance of athermoelectric module as function of the current passing through thethermoelectric module for various temperature differentials;

FIG. 10 is a graph illustrating the effects of evaporative cooling ofthe waste gas; the graph is depicted in terms of cooling power andcoefficient of performance verses electric power; and

FIG. 11 is a graph which demonstrates the effects of the evaporativecooling of the waste gas; the graph depicts electric power andcoefficient of Performance verses cooling power.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, FIG. 2 and FIG. 4, a thermoelectric device 10includes a first fluid conduit 11 and at least two thermoelectricmodules 12, each having a first side 13 and a second side 14. The firstside 13 of all thermoelectric modules 12 are in parallel thermal contactwith first fluid conduit 11, and a second fluid conduit 15 which isdivided into a plurality of sections 16. Each section 16 is in thermalcontact with a second side 14 of only one of the thermoelectric modules12.

Thermoelectric modules 12 are recessed in a gasket plate 17, which ispreferably made of a thermally insulative material, such that first side13 is substantially co-planer with one side of gasket plate 17 and thesecond side 14 is substantially co-planer with the opposite side ofgasket plate 17. Gasket plate 17 and the thermoelectric modules 12 arepositioned between first fluid conduit 11 and second fluid conduit 15.Each section 16, the thermoelectric module 12 that is in thermal contacttherewith, and first fluid conduit 11 may be compressed against eachother by a compression means which may be adjusted to achieve optimumconditions for thermal transfer between section 16 and first fluidconduit 11. The interface of the section 16 and the first fluid conduitmay be coated with a thermal grease or other similar joint material toeffect a thermally conductive interface.

Preferably, thermoelectric modules 12 are of the type readily availablein the industry. Such modules may be a thermoelectric couple whichincludes a n-type element and a p-type element. Multiples of thesecouples are assembled electrically in series and thermally in parallel.The multiple couples are sandwiched between two flat plates that areelectrically insulating and thermally conducting. The n-type and p-typeelements are typically constructed respectively from semiconductormaterial, such as N-type bismuth telluride and P-type bismuth telluride.CP series Melcor brand thermoelectric modules which are available fromMelcor Materials Electronic Products Corporation of Trenton, N.J. are anexample of thermoelectric modules that may be used in the invention.

The preferred construction of first fluid conduit 11 and sections 16 isof a thermally conductive material, such as aluminum, which formschannels 18 within which the media, usually either a gas or liquid,which is being cooled or heated flows. For purposes of illustration itwill be assumed hereinafter that this flow in both conduits is a gas. Itshould be understood that where gas is indicated, a liquid may also beutilized in other applications.

Longitudinal fins 19 may be located within the channels 18 to increasethe efficiency of thermal transfer. In the installed configuration ofthe invention it is preferred that the fins 19 of the first conduit 11be oriented in an upright, e.g. vertical orientation. This particularorientation facilitates the evacuation of condensate which may form outof the first gas flow as the temperature of that gas flow approaches thedew point temperature. It is preferred that the fins 19 be oriented suchthat the evacuation of the condensate may be accomplished by reliance onthe force of gravity.

Although channel 18 of first fluid conduit 11 and channel 18 of section16 may be oriented relative to each other such that the media flow infirst fluid conduit 11 and media flow in section 16 are parallel to eachother, the preferred orientation is for perpendicular media flow, asillustrated in the drawings. The perpendicular orientation is thecross-flow configuration.

In the illustrated embodiment of the invention, the compression means isa stud 20 having a biasing means, such as stud belville washers 21 andstud nuts 22 on each end of stud 20. The biasing means may be tightenedto apply the desired compressive force. Stud 20 may extend through apair of thermoelectric devices 10, thereby connecting them together andreducing by half the number of studs 20, stud belville washers 21 andstud nuts 22 required for assembly. Preferably studs 20 pass through ahole 23 in the center of the thermoelectric modules 12 and throughprotective sleeves 24.

Referring to FIG. 1, FIG. 2, FIG. 3 and FIG. 4, a pair of thermoelectricdevices connected to another pair of thermoelectric devices and endplates 25 placed across sections 16 which are not mated to othersections 16 form a thermoelectric subunit 26. Thermoelectric subunit 26is held together with assembly rods 27, which, in each pair ofthermoelectric devices, pass through end plate 25, groves 28 which liebetween sections 16, gasket plate 17 and first heat exchanger 11.Assembly rods 27 have a biasing means, such as a assembly belvillewasher 29 and a assembly nut 30 attached to each of the ends of assemblyrods 27, to maintain a constant compressive force across thermoelectricsubunit 26.

Referring to FIG. 2 and FIG. 3, a plurality of thermoelectric subunits26 may be associated with each other to form a cross-flow thermoelectricapparatus 31. The heating and cooling capacity of thermoelectricapparatus 31 is dependant upon the number of thermoelectric modules 12which are used in the thermoelectric apparatus 31. In the illustratedembodiment, a layer of thermoelectric subunits 26 is formed by buttingthe ends of two or more thermoelectric subunits 26 together. Two or morelayers of thermoelectric subunits 26 are then stacked upon one anotherto form cross-flow thermoelectric apparatus 31. The surfaces where heatexchangers 11 of one thermoelectric device 10 mate with fluid conduits11 of another thermoelectric device 10, where sections 16 of onethermoelectric device 10 mate with sections 16 of another thermoelectricdevice 10 or with end plates 25. Where the fluid conduits of onethermoelectric subunit mate to the fluid conduits of anotherthermoelectric subunit, the conduits are preferably sealed with gasketmaterial 32 to minimize leakage of the media flowing through first fluidconduit 11 and second fluid conduit 15.

It is preferable to retain the cross-flow thermoelectric apparatus 31within a frame (not illustrated) which utilizes horizontal biasing means(also not illustrated) to maintain positioning of thermoelectricsubunits 26. Cross-flow thermoelectric apparatus 31 can be servicedquickly and efficiently because the failure of a thermoelectric module12 requires only the replacement of a thermoelectric subunit 26, and notthe complete disassembly of cross-flow thermoelectric apparatus 31.

Referring to FIG. 5, an application of the thermoelectric device forheating or cooling parked aircraft is schematically illustrated. Priorto the arrival of an aircraft, cross-flow thermoelectric apparatus 31 isconnected to a first fan 33 which circulates air through a closedcircuit consisting of first fan 33, first fluid conduit 11, output duct34, air reservoir 35 and return duct 36, and the air in the closedcircuit is brought to the desired temperature. Preferably, air reservoir35 is the passenger boarding bridge to which the aircraft will dock,both ends of which are closed by doorways prior to the arrival of theaircraft. After the arrival of the aircraft, the aircraft is added tothe closed circuit through diversion duct 37 by the changing of positionof damper 38. The parked aircraft is then cooled or heated through theuse of the precooled or preheated air produced by the instant invention.This heating or cooling is assisted by the use of the precooled orpreheated air which has been stored in air reservoir 35. Ambient air isintroduced into the heretofore closed circuit by means of inlet 36Aduring the course of the operation of the apparatus in order to producean air mixture adapted for meeting and maintaining ASHRAE fresh airstandards. Ambient air is forced through the second fluid conduits 15 bysecond fan 39 to provide fresh flow of ambient air through thethermoelectric apparatus 31. In FIG. 5 the second fan 39 is illustratedas being placed in the second conduit 15 upstream of that conduit'sassociation with the thermoelectric apparatus 31. In an alternativeconstruction, the fan 39 is placed in the second conduit downstream ofthe association of that conduit with the thermoelectric apparatus 31.This latter placement of the second fan permits the invention to avoidadding heat to the flow in the second conduit due to the operation ofthe second fan at a location upstream of the association of the secondconduit with the thermoelectric apparatus 31. In this latter fanplacement, the air is drawn through the second conduit and through thethermoelectric apparatus by the vacuum created by the second fan,instead of being forcefully and positively being driven through theapparatus by a fan placed upstream of the apparatus. This latterconstruction thereby avoids the possibility of raising the temperatureof the second fluid flow, due to the action of the second fan, prior tothe fluid's passage through the thermoelectric apparatus 31.

FIGS. 6 and 6A illustrate an embodiment of the thermoelectric device 31of the invention in which each thermoelectric module 12 is adapted toreceive an individually determined quantity of electrical power for itsoperation. The invention also contemplates that discrete groups ofmodules, as opposed to individual modules, may be supplied with anindividually determined quantity of electrical power for theiroperation. It should be understood therefore that in the followingdescribed embodiment, where a reference is made to a thermoelectricmodule, in other embodiments the thermoelectric module could be replacedby a group of thermoelectric modules.

The quantity of power which is supplied to each thermoelectric module 12is determined by analyzing the temperature differential between thetemperature of the thermoelectric material at the junction of thethermoelectric module with the first fluid conduit 11 and thetemperature of the thermoelectric material at the junction of thethermoelectric module with the second fluid conduit.

As shown in FIG. 7 the temperature of the thermoelectric material at thejunction of the module 12 with the first fluid conduit 11, designated inFIG. 6 as Tc, decreases with an increasing negative slope with eachsucceeding module 12 as one proceeds along the length of the fluidconduit 11. It is assumed that the temperature of the thermoelectricmaterial at the junction of the module with the second fluid conduit 15,herein designated as Th remains constant for each of the modules 12 overthe corresponding length of the fluid conduit 15.

Noticeably, delta T, the temperature differential between Tc and Thincreases over the length of the first fluid conduit. As shown, delta Tis increasing over the aforesaid length with a decreasing slope. Forpurposes of the instant example, the ambient temperature is assumed tobe 40 degrees Celsius (C). The final temperature of the gas in the firstfluid conduit is 10 degrees C. As depicted in FIG. 8 the heat pumpcapacity of a thermoelectric module increases at constant current fordecreasing values of delta T. It follows that thermoelectric modules aremost efficient when the delta T between the temperatures of the opposingfaces of the thermoelectric material and hence the differential betweenthe temperatures of the two gases on the opposing sides of thethermoelectric module is minimized.

FIG. 9 illustrates that thermoelectric modules achieve a maximumcoefficient of performance for a given delta T. As used herein theterminology "coefficient of performance" (COP) shall be understood tomean the ratio of cooling or heating power divided by electrical inputpower. The curves illustrated in FIG. 9 were generated by means of theexpression: ##EQU1## where ΔT_(m) =1/2ZT_(c) ²

i=the electrical current

Z=The Figure of Merit of the thermoelectric material as definedhereinafter.

Utilizing this information, the instant invention achieves enhancedperformance characteristics by individually adjusting the currentpassing through each thermoelectric module. The amount of currentsupplied to each thermoelectric module is determined by identifying themaximum coefficient of performance from the graph in FIG. 9 for thetemperature differential across each particular thermoelectric module12. Recognizing that delta T increases along the length of the first gasconduit in the direction of the flow in that conduit, it will beappreciated that the optimum current input for each subsequent modulealong the length of the first gas conduit will increase along the lengthof that conduit in the same direction of flow.

In the illustrated embodiment, the delta T is for determined for a giventhermoelectric module 12 by initially taking a temperature reading ofthe thermoelectric material at the junction of the thermoelectric moduleand the first conduit as well as a temperature reading of thethermoelectric material at the junction of the thermoelectric module andthe second conduit. These temperature readings are obtained by means ofsensors 42. These sensors may be of conventional construction, e.g. aconventional electrically powered thermocouple. As illustrated aplurality of sensors 42a is positioned along the array of modules 12.Each sensor 42a is paired with a respective thermoelectric module 12 andis located on the module at a location proximate the mounting of itsrespective thermoelectric module 12 to the conduit 11. A plurality ofsensors 42b is also mounted along the array of modules. Each sensor 42bis paired with a respective module 12 and is mounted on its module at alocation proximate the mounting of its respective thermoelectric module12 to the conduit 15. Each sensor 42a is preferably paired with arespective sensor 42b, whereby each pair of sensors samples thetemperature of the thermoelectric module at both of its opposing faces.

The sensors 42 may be connected to a computation means 43, which may bea conventional microprocessor programmed to receive signals from thevarious sensors. The computation means is further adapted to compare thetemperature readings for each pair of sensors 42a and 42b for eachrespective thermoelectric module 12 and determine a temperaturedifferential or delta T for each thermoelectric module. Once the delta Thas been determined for a particular thermoelectric module, thecomputation means is programmed to determine the peak value of thecoefficient of performance for the particular delta T. Determination ofthis peak value identifies the optimum current which should be suppliedto the particular thermoelectric module in order to achieve optimalperformance by that thermoelectric module. Because optimalthermoelectric performance by the thermoelectric modules may not producethe required cooling power for a given application, it should beunderstood that for various reasons the user may elect to operate themodules at current inputs within a predetermined range about thedetermined peak value. In many embodiments of the invention themicroprocessor is further programmed to calculate an operating current(I) for each thermoelectric module.

In a preferred method, this operating current (I) is found within arange which extends between the value for the optimum current (Iopt) andthe value for the maximum current (Imax).

For a given application of the invention, initially a desired coolingpower is provided. The temperatures Th and Tc are either estimated orsensed for each thermoelectric module. For each module or group ofmodules, a quantity I_(opt) is determined by the microprocessor by usingthe following formula: ##EQU2## wherein k is the thermal conductivity ofthe thermal electric material of the thermal electric module;

ΔT=[T_(n) -T_(c) ];

Z=the figure of merit of the thermal electric material which may beexpressed as: ##EQU3## wherein s is the Seebeck coefficient, ρ is theelectrical sensitivity of the thermal electric material and k is thethermal conductivity of the thermal electric material;

s=the Seebeck coefficient;

T is the average temperature of the thermal electric material, i.e. andλ=l/α where l=length of the thermal electric material and a is thecross-sectional area of the thermal electric material.

For each module or group of modules the quantity I_(max) is thendetermined. I_(max) is defined by the expression ##EQU4## wherein thevariables K, ΔT, Z, T, S and λ are defined as set forth above. Theoperating current I to be supplied to each module or group of modules isthen calculated by the microprocessor by using the following expression:

    I=I.sub.opt +β(I.sub.max -I.sub.opt)

where β may be varied from 0.0 to 1.0

In one method β is initially set at 0.5. A respective value for I isthen calculated for each module or group of modules by themicroprocessor.

Each thermoelectric module is wired to a current regulator 46. Thecurrent regulator 46 is also interconnected to the microprocessor 43.The microprocessor is programmed to relay a command to the regulator 46to cause the regulator to supply a quantity of electrical current toeach particular thermoelectrical module in an amount corresponding tothe particular quantity of current I which the microprocessor hascalculated for that particular thermoelectric module.

The amount of current supplied to each module is therefore equal to thevalue of I calculated for that respective module. With eachthermoelectric module operating at its respective I current, thetemperature of the air exiting the first fluid conduit 11, hereinafterdenoted as Texit is sensed i.e. sampled by a conventional temperaturesensing apparatus, e.g. a thermometer. Texit is then compared to the airtemperature Tcal which has been calculated, pursuant to formulas wellknown in the art, as being the exit temperature required to achieve therequired cooling power for the given application. If the temperature ofthe air exiting the cooling system Texit is below the calculatedtemperature Tcal., then the value of β is decreased by a preselectedincrement, e.g. 0.05. The respective value of I for each of thethermoelectric elements are then recalculated using the new value for β.Thereafter current corresponding to the new I values is suppliedrespectively to the various thermoelectric modules by the microprocessorcontrolled current regulator 46. The exit temperature Texit is thentaken again and compared to the Tcal. If Texit is less than Tcal., β isthen decreased again by a selected increment, e.g. 0.05. If Texit isgreater than Tcal, β is increased by a selected increment, e.g. one halfof the increment which was previously added to β to achieve the thenpresent value of β. In both cases I is then recalculated again using thenew value for β. The quantity of current corresponding to the nextgeneration of I values is then supplied to the respective modules andthe temperature Texit is again sampled. The value of Texit is then againcompared to Tcal. The above process of either increasing β or decreasingβ and recalculating β is then repeated together with the subsequentrecalculations of I and the accompanying regulation of currents I to therespective modules.

This process is continued on an iterative type approach until theapparatus achieves a set of values for I which results in an exittemperature equal to the calculated temperature value Tcal.

The instant apparatus may include a microprocessor adapted tocontinuously sense, i.e. sample the temperatures of the thermoelectricmodules and thereafter compare those temperatures with the respectivevalues for I. Alternatively, the microprocessor can be programmed tosense, i.e. sample, the temperatures of the various thermoelectricmodules at predetermined time intervals, e.g. every minute, andthereafter compute the respective I values.

While it is specifically indicated that the temperatures of thejunctions of the thermoelectric module with the first conduit and thesecond conduit are sampled for computational purposes, it should beunderstood that alternative temperature readings may be substituted forthe temperature readings at the above said junctions. For example, aconventional air temperature apparatus could be used to sense thetemperature of the fluid flow in each conduit proximate the junction ofthe conduit with each respective thermoelectric element. Alternatively,a thermocouple or other temperature sensing apparatus could be used tosense the temperature of the conduit sidewall for each conduit at alocation proximate the junction of each conduit with each respectivethermoelectric element. It should be understood that the temperature ofthe fluid in the conduit and the temperature of the thermoelectricmaterial at the junction of the conduit with the thermoelectric materialshould all be within 15° C. of one another.

It should be appreciated that it is the temperatures on the opposingfaces of the thermoelectric material which are critical to calculatingthe values for the current I. Sensing the temperatures of either thefluid flow or the conduit sidewalls may be used as a means ofapproximating the temperatures of the opposing faces of thethermoelectric material. Accordingly, these alternative temperaturereadings produce less accurate, but nevertheless acceptable temperatureapproximations for purposes of determining the values for I. Sensing theinlet and outlet temperatures of the two fluid conduits, would alsoprovide a sufficient data base from which the I values could bedetermined. It is further recognized that other temperature readingscould also be used to approximate the temperatures of the opposing facesof the thermoelectric material.

The computation means, e.g. a microprocessor, is intercooperated with acontrol means, e.g. the current regulator 46 which is adapted to supplythe operating current to each particular thermoelectric module 12. Itshould be recognized that the present system can be constructed andprogrammed to permit the temperatures monitored by sensors 42 to be readperiodically at predetermined intervals. Alternatively, the system canbe constructed to permit continuous monitoring of the aforesaidtemperatures. Further, the computation means can be constructed topermit either periodic or continuous computation of optimum currentvalues. Moreover, the control means can also be constructed to permitcontinuous or periodic regulation of the current being supplied to thethermoelectric modules. It follows that the current system can beutilized to provide a means of continuously optimizing the individualoperational characteristics of each thermoelectric module responsive tothe changes in the temperature differential extant within a determinedspatial ambit of the particular thermoelectric module. The instantinvention therefore avoids the inefficiencies which would result fromproviding a uniform current to each thermoelectric module in the arrayand instead the instant system maximizes the operational characteristicsof the thermoelectric modules by restricting their power consumption tothose current levels which yield a maximum heat transfer.

Referring again to FIG. 5, a moisture means 48 is illustrated as beingassociated with the second fluid conduit 15. This moisture means may bea plurality of injectors connected to a source of water, which may bepressurized. Alternatively, the moisture means may be any otherstructure adapted for introducing water into a flow stream. In oneembodiment of the invention, the water which is removed from the firstgas flow in the form of condensate is collected as it drains from thefins of the conduit 11, and thereafter directed to the moistureintroduction means for purposes of its introduction into the second gasflow.

When water is introduced into the gas flow in the second conduit 15, thewater absorbs heat which is contained in the air flow. The absorption ofthat heat by the water tends to lower the temperature of the air in thesecond gas flow. The heat is absorbed by the water until the quantity ofheat reaches the quantity corresponding to the latent heat ofvaporization for the water. At this point the water is vaporized.

Depending on the temperature of the air in the second gas flow, thewater may be vaporized prior to the entry of the gas flow into thatsection of the second conduit which is in contact with thethermoelectric modules. With the water being totally vaporized prior tothe second gas flow being affected by the thermoelectric modules, thesecond gas flow reaches the thermoelectric modules at a considerablyreduced temperature due to the effect of the water absorbing the heatfrom the gas flow.

In the event that the water is not completely vaporized by the time itreaches the section of the second conduit associated with thethermoelectric modules, and that second gas flow is subsequently broughtinto contact with the sidewalls of the second conduit which has beenheated by a thermoelectric module 12, heat from that sidewall isabsorbed by the second gas flow and more particularly by the water inthat second gas flow. This absorption of the heat by the water occurswithout an accompanying increase in the temperature of the second gasflow. Since the thermoelectric modules, according to the conclusionsillustrated in FIG. 8 achieve higher heat pumping capabilities at lowervalues of delta T, it follows that constraining any increase in thetemperature of the second gas flow in the second fluid conduit tends tomaximize the operational heat pump characteristics of the thermoelectricmodules 12. Accordingly, the use of the moisturized air tends tooptimize the effectiveness of the thermoelectric modules by minimizingthe delta T across the modules.

FIGS. 10 and 11 illustrate the benefits of introducing moisture, andparticularly water, into the second gas flow in conduit 15 upstream ofthat conduit's connection to the thermoelectric modules 12. The twographs reflect computed data from two systems which each included afirst fluid conduit, a second fluid conduit and a plurality ofthermoelectric modules arranged according to the manner described above.The sole distinguishing feature which separated the two systems was theuse in one of the systems of a moisture introduction means as previouslydescribed. As shown in FIG. 10 the coefficient of performance for asystem which utilizes the evaporative cooling which results from the useof such moisture introduction means is significantly increased over anidentical system, for identical power consumption, which does notinclude evaporative cooling of the second gas in the second fluidconduit. Notably, the cooling power of the system which utilizesevaporative cooling, is also significantly larger than the system whichdoes not include such a system, at constant power consumption.

FIG. 11 illustrates that a system utilizing evaporative cooling obtainssignificant reductions in power consumption for a given cooling powerrequirement. Further, FIG. 11 also indicates that the system fitted withan evaporative cooling means also achieves enhanced coefficient ofperformance, especially at low cooling power requirements.

It should be understood that an evaporative cooling of the waste gas,i.e., the gas in the second fluid conduit, may also be incorporated withthe previously described embodiment which utilizes a variability in thecurrent supplied to each of the thermoelectric modules to achieveenhanced operational characteristics.

While the previously described apparatus has been described for purposesof producing a supply of cooled air for human use, it should beunderstood that a reversal of the polarity of the thermoelectricelements would result in the production of heated as opposed to cooledair through the first conduit 11.

Whereas the invention is here illustrated and described with specificreference to an embodiment thereof presently contemplated as the bestmode in carrying out such invention, it is to be understood that variouschanges may be made in adapting the invention to different embodimentswithout departing from the broad inventive of concepts disclosed hereinand comprehended by the claims that follow.

What is claimed is:
 1. A thermoelectric unit for cooling or heating agas, said thermoelectric unit comprising:a first conduit adapted todirect a first gas flow; a second conduit adapted to direct a second gasflow; a plurality of thermoelectric modules each of which is operativelyconnected between said first and second conduits so as to transfer heatfrom the first gas flow to the second gas flow; and a plurality ofregulated power sources, each of which supplies a different amount ofpower to a corresponding different one said plurality of thermoelectricmodules.
 2. The thermoelectric unit of claim 1 further comprising acontroller individually controlling the operation of each of theplurality of regulated power sources so as to supply the differentamounts of power to each of the plurality of thermoelectric modules. 3.The thermoelectric unit of claim 2 further comprising a plurality ofsensors each of which senses a temperature differential across acorresponding different one of said plurality of thermoelectric modules,and wherein the controller individually controls the operation of eachof the plurality of regulated power sources based on the sensedtemperature differential across the thermoelectric module correspondingto that power source.
 4. The thermoelectric unit of claim 3 wherein saidcontroller comprises a computer programmed to compute an operatingcurrent for each of said plurality thermoelectric modules based on thetemperature differential across that thermoelectric module, and whereineach of the regulated power sources supplies the computed operatingcurrent to its corresponding thermoelectric module.
 5. Thethermoelectric unit of claim 4 wherein the operating currents for thethermoelectric modules increase in the direction of gas flow through thefirst passageway.
 6. The thermoelectric unit of claim 4 wherein each ofthe plurality of thermoelectric modules comprises a thermoelectricmaterial having opposed faces and wherein each of said plurality ofsensors senses a temperature differential across the opposed faces ofthe thermoelectric material in the corresponding thermoelectric module.7. The thermoelectric unit of claim 4 further comprising a temperaturemeasuring device measuring an exit temperature for the first passageway,said exit temperature being the temperature of gas exiting from thefirst passageway, and wherein said controller is programmed toiteratively adjust the operating currents supplied to each of saidthermoelectric modules by its corresponding power source so as toachieve a desired value for the measured exit temperature.
 8. Thethermoelectric unit of claim 2 further comprising an upstream sensor anda downstream sensor, wherein the upstream sensor senses a temperature atan upstream location within the first gas flow and the downstream sensorsenses a temperature at a downstream location within the first gas flowand wherein said controller comprises a computer programmed to use thesensed upstream and downstream temperatures to compute a temperaturedifferential across each of said plurality of thermoelectric modules,and wherein the controller individually controls the operation of eachof the plurality of regulated power sources based on the computedtemperature differential across the thermoelectric module correspondingto that power source.
 9. The thermoelectric unit of claim 4 for coolingor heating a gas within a first and second reservoir, wherein the firstreservoir is coupled to the second reservoir so that the gas may flowfrom one to the other, said thermoelectric unit further comprising:anoutput duct connected to an outlet side of the first conduit, saidoutput duct adapted to be connected to the first reservoir so as todirect the first gas flow into the first reservoir; a return ductconnected to an inlet side of the first conduit, said return ductadapted to be connected to the first reservoir so as to return the firstgas flow from the first reservoir to the first conduit; a damperconnected between the output duct and the outlet side of said firstconduit, said damper having a closed position in which the first gasflow is directed into the output duct and an open position in which atleast a portion of the first gas flow is diverted away from the outputduct; and a diversion duct connected to the damper, said diversionadapted to be connected to the second reservoir so as to direct thediverted gas flow into the second reservoir.
 10. The thermoelectric unitof claim 4 for cooling or heating a gas within a reservoir, saidthermoelectric unit further comprising:an output duct connected to anoutlet side of the first conduit, said output duct adapted to beconnected to the reservoir so as to direct the first gas flow into thefirst reservoir; and a return duct connected to an inlet side of thefirst conduit, said return duct adapted to be connected to the reservoirso as to return the first gas flow from the first reservoir to the firstconduit.
 11. The thermoelectric unit of claim 4 further comprising amoisture injector associated with the second conduit and for injectingmoisture into the second gas flow.
 12. The thermoelectric unit of claim11 wherein the moisture injector injects moisture into the secondconduit upstream of said plurality of thermoelectric modules.